Fuel vapors comprise vaporized hydrocarbons (HCs) that contribute to the formation of hazardous ground-level ozone. Accordingly, vehicles may be fitted with evaporative emission control systems to reduce the release of fuel vapors to the atmosphere. For example, vaporized HCs from a fuel tank may be stored in a fuel vapor canister packed with an adsorbent which adsorbs and stores the vapors. At a later time, when the engine is in operation, the evaporative emission control system allows the vapors to be purged into the engine intake manifold for use as fuel.
During a purge operation, a canister purge valve coupling the canister and the engine is opened, and the engine vacuum is utilized to draw ambient air into the canister via a canister vent line to release the stored hydrocarbons. However, if a vehicle is operating in an area where the ambient hydrocarbon levels are high, during purging, the ambient air drawn into the canister may not efficiently release the stored hydrocarbons. Consequently, instead of purging the stored hydrocarbons, ambient air may be purged into the intake manifold, which may lead to operating the engine at a more lean air to fuel ratio than desired. As a result, fuel economy may be reduced, and exhaust emissions may increase. Further, if the stored hydrocarbons are not purged, the canister may become saturated and may not be able to adsorb any additional fuel vapors that are generated. Consequently, the fuel vapors may be released into the atmosphere leading to degraded evaporative emissions control system performance.
The inventors herein have recognized the above issues, and have developed systems and methods to at least partially address them. In one example, a method comprises: in response to an ambient hydrocarbon amount estimated during purging fuel vapors from a canister to an engine being greater than a threshold, terminating the purging by closing a canister purge valve; and sealing the canister from the ambient air by closing a canister vent valve. In this way, by terminating a purging operation and sealing the evaporative emissions system when ambient hydrocarbon levels are high, purging of ambient air may be reduced and hydrocarbon breakthrough to the atmosphere may be reduced.
For example, during purging fuel vapors from the canister, an ambient hydrocarbon amount may be estimated based on an output from a hydrocarbon sensor located in a canister vent line through which ambient air is drawn into the canister. If the estimated hydrocarbon amount is greater than a threshold amount, poor ambient air quality may be inferred. Accordingly, the purging is terminated by closing a canister purge valve, and the evaporative emissions control system is sealed by closing a canister vent valve located in the canister vent line. Further, a vehicle climate control system is adjusted so that only air from the vehicle cabin is recirculated and no fresh air is provided to the vehicle cabin. By providing full cabin air recirculation, the vehicle cabin may be insulated from poor air quality. Still further, in an engine system equipped with a direct fuel injector and a port fuel injector for each engine cylinder, in response to estimating ambient hydrocarbon levels greater than the threshold, engine operation may be adjusted to increase a ratio of a port injected fuel amount to a direct injected fuel amount in order to reduce particulate matter emissions.
In this way, a hydrocarbon sensor located in the canister vent line may be utilized to detect an ambient hydrocarbon amount during purging. If high ambient hydrocarbon amounts are detected, vehicle operations may be adjusted to reduce purging ambient air, reduce hydrocarbon breakthrough, reduce exposure of vehicle occupants to poor air quality, and reduce particulate emissions.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.